Photo-voltaic element and method of manufacturing the same

ABSTRACT

A photo-voltaic element ( 1 ) comprising a stack of layers is provided. The stack of layers at least includes the following layers arranged in the order named: a first electrode layer, a first charge carrier transport layer, an insulating layer, a second electrode layer, a second charge carrier transport layer, and a photo-electric conversion layer. The photo-electric conversion layer ( 70 ), comprises a plurality of distributed extensions ( 72 ) extending through the second charge carrier transport layer ( 60 ), the second electrode layer ( 50 ) and the insulating layer ( 40 ) to the first charge carrier transport layer (30). The extensions ( 72 ) have an effective cross-section D eff  in the range of 0.5 to 10 micron, and have an average pitch in the range of 1.1 to 5 times said effective cross-section.

BACKGROUND OF THE INVENTION Field of the invention

The present invention pertains to a photo-voltaic element. The presentinvention further pertains to a method of manufacturing the same.

Related Art

A photo-voltaic element is disclosed in CN105140398 that comprises aconductive substrate; a uniform electron transport layer; a dielectriclayer; a metal layer; and a perovskite layer as a photo-electricconversion layer. The latter has a plurality of channels through thedielectric layer and the metal layer that contact the electron transportlayer. Accordingly the perovskite photo-electric conversion layer hasits electric contacts for delivering electrical energy at the same side.Therewith it can be avoided that light to be converted has to passthrough an electrode layer, as a result of which it would be attenuatedbefore conversion.

The cited document also presents a method of manufacturing thephoto-voltaic element disclosed therein. Therein a substrate is providedof a transparent conductive glass and an electron transport layer isdeposited thereon by magnetron sputtering ZnO. Subsequently a layer ofdispersed PS pellets having an original diameter of 2 um is depositedresulting in a hexagonal close-packed structure of said PS pellets. ThePS ball diameter is subsequently reduced to 1 um by dry etching usingRIE. A dielectric layer of Al2O3 is deposited thereon using ALDdeposition followed by magneton sputtering of an Au layer. Subsequently,using a solvent and an ultrasonic treatment the PS pellets and theportions of the Al2O3 layer and the Au layer deposited thereon areremoved, so that an Au mesh is obtained that is insulated from theelectron transport layer. A perovskite layer is spin coated thereon thatboth contacts the Au mesh and the ZnO electron transport layer.

It is a disadvantage of this known process, a lift-off process, that thepatterning process is not well controlled. As a result the boundaries ofthe openings in the insulator layer and the upper electrode layer arejagged and an unreliable or even non-working product is obtained.

It is noted that WO2017/060700, published after the priority date ofthis document also uses a lift-off process. As shown for example in FIG.2, subsequently:

the patterned resist layer is formed on the lower electrode (a)

the insulator and HCE layer are deposited thereon (b)

the patterned resist layer and the portions of the insulator layer andHCE layer present thereon are removed in the lift-off step (c).

SUMMARY OF THE INVENTION

It is a first object of the invention to provide a photo-voltaic elementwith an improved conversion efficiency.

It is a second object of the invention to provide a method ofmanufacturing this improved photo-voltaic element.

In accordance with said first object, according to a first aspect, aphoto-voltaic element is provided as claimed in claim 1.

In accordance with said second object, according to a second aspect, amethod of manufacturing a photo-voltaic element is provided as claimedin claim 8.

The photo-voltaic element is provided as claimed in claim 1 comprises astack of layers that at least include in the order named: a firstelectrode layer, a first charge carrier transport layer, an insulatinglayer, a second electrode layer, an second charge carrier transportlayer, and a photo-electric conversion layer.

The first electrode layer is provided for receiving charge carriers of afirst polarity, for example electrons, or alternatively for receivingholes as the charge carrier. The first charge carrier transport layer isprovided for transport of charge carriers having the first polarity.E.g. if the first electrode layer is a cathode provided for receivingelectrons as the charge carrier then the first charge carrier transportlayer is an electron transport layer. Alternatively, if the firstelectrode layer is an anode provided for receiving holes as the chargecarrier then the first charge carrier transport layer is a holetransport layer. The insulating layer may be provided of anysufficiently insulating organic or inorganic material. The secondelectrode layer is provided for receiving charge carriers of a secondpolarity opposite to the first polarity. Hence if the first electrodelayer is a cathode then the second electrode layer is an anode and viceversa. The second charge carrier transport layer is provided fortransport of charge carriers having the second polarity. Accordingly thesecond charge carrier transport layer is a hole transport layer if thesecond electrode layer is an anode and an electron transport layer ifthe second electrode layer is a cathode. The photo-electric conversionlayer comprises a plurality of distributed extensions that extendthrough the second charge carrier transport layer, the second electrodelayer and the insulating layer to the first charge carrier transportlayer.

Because the photo-electric conversion layer is the uppermost layer ofthe stack (apart from e.g. a protection layer or encapsulation), it isnot necessary that the various layers are transparent. Therewith one ormore of the electrodes may be formed as a metal layer, for example analuminum or a copper layer, possibly sandwiched between intermediatelayers, e.g. as MoAlMo or CrCUCr. Nevertheless, embodiments may becontemplated wherein a transparent electrically conductive material isused for the electrodes, for example a transparent electricallyconductive oxide like ITO. This is advantageous in that the device soobtained is bilaterally sensitive. Alternatively, this may be combinedwith a substrate having a reflecting surface. In this embodiment, lightentering the device that is not converted in the photo-electricconversion layer is reflected back to the latter, so that it can stillbe (partially) converted.

Therewith the photo-electric conversion layer is electrically coupled toboth the first charge carrier transport layer and the second chargecarrier transport layer. In this arrangement solar radiation R does notneed to traverse an electrode layer or a charge carrier transport layer,which contributes to an efficient operation of the photo-voltaicelement.

An optimal conversion efficiency is achieved by the presence of a chargecarrier transport layer between the first electrode layer and thephoto-electric conversion layer as well as between the second electrodelayer and the photo-electric conversion layer.

The extensions have an effective cross-section D_(eff) in the range of0.5 to 10 micron, and have an average pitch in the range of 1.1 to 5times their effective cross-section. The effective cross-section isdefined here as the diameter of a circle having an area corresponding tothe cross-sectional area A_(Ø) of the extensions.

${I.e.\mspace{14mu} D_{eff}} = \sqrt{\frac{4A_{\Phi}}{\pi}}$

The extensions are typically cylindrical. Alternatively the extensionsmay taper inward or outward. The extensions may have any cross-section,such as circular, square or triangular. The circumference O of theextensions is less than 10 times the effective diameter D_(eff) andpreferably less than 5 times the effective diameter D_(eff). Therewithan optimum contact surface between the photo-electric conversion layerand the first charge carrier transport layer is achieved with minimumdisruption of the intermediary layers, in particular the secondelectrode layer and the second charge carrier transport layer.

In an embodiment of the photo-voltaic element the extensions taperoutward in a direction from the first charge carrier transport layer tothe second charge carrier layer.

In an embodiment thereof, material of the second charge carriertransport layer covers a surface of the second electrode surrounding theextensions. Therewith a contact surface provided for the photovoltaiclayer is improved.

In an embodiment, the first charge carrier layer is absent in areas ofthe first electrode layer covered by the insulating layer. Also in thiscase, the stack formed in the product is deemed to comprise first chargecarrier layer and a subsequent insulating layer, as the surface of theinsulating layer will be above a surface of the first charge carrierlayer, when traversing the layers starting from the substrate on whichthe layers are deposited.

In an embodiment the photo-electric conversion layer is provided of aperovskite material. Perovskite materials typical have a crystalstructure of ABX₃, wherein A is an organic cation as methylammonium(CH₃NH₃)⁺, B is an inorganic cation, usually lead (II) (Pb²⁺), and X isa halogen atom such as iodine (I⁻), chlorine (Cl⁻) or bromine (Br⁻).Perovskite materials are particularly advantageous in that they can beprocessed relatively easily and in that their bandgap can be set to adesired value by a proper choice of the halide content. A typicalexample is methylammonium lead trihalide (CH₃NH₃PbX₃), with an opticalbandgap between 1.5 and 2.3 eV depending on halide content. Another morecomplex structure example is Cesium-formamiclinum lead trihalide(Cs_(0.05)(H₂NCHNH₂)_(0.95)PbI_(2.85)Br_(0.15)) having a bandgap between1.5 and 2.2 eV. Other metals such as tin may replace the role of Pb inperovskite materials. An example thereof is CH₃NH₃SnI₃. Alsocombinations of Sn with Pb perovskites having a wider bandgap in therange of 1.2 to 2.2 eV are possible. In another embodiment thephoto-electric conversion layer is made of copper indium galliumselenide (CIGS).

The geometry of the substantially circular cylindrical extensions withan effective cross-section D_(eff) in the range of 0.5 to 10 micron, andwith an average pitch in the range of 1.1 to 5 times their effectivecross-section makes it possible to optimally tune the contact-surface ofthe photo-voltaic layer with the first and the second charge carriertransport layer respectively dependent on the type of perovskitematerial used for the photo-voltaic layer. This is favorable, in thatthe ratio of mobility for holes and electrons may differ. E.g. if for acertain perovskite the mobility of electrons is 3 time higher than forholes, the surface area of the HTL preferably is approximately 3× thesurface area of the ETL for an optimal efficiency.

The method as claimed in claim 13 enables manufacturing thephoto-voltaic element of claim 1. The claimed method comprises the stepsof:

providing a substrate;

depositing thereon a stack of layers comprising at least in the ordernamed:

-   -   a first electrode layer for receiving charge carriers of a first        polarity;    -   an insulating layer;    -   a second electrode layer for receiving charge carriers of a        second polarity opposite to said first polarity; wherein the        insulating layer and layers subsequently deposited in this step        form a sub-stack having an upper surface,

applying a resist layer on said upper surface, wherein said resist layeris provided with a plurality of distributed openings towards said uppersurface, the openings having an effective cross-section D in the rangeof 0.5 to 10 micron, and having an average pitch in the range of 1.1 to5 times said effective cross-section,

etching to selectively remove material of the sub-stack facing theopenings,

removing the resist layer subsequent to said etching,

depositing and curing a photo-electric conversion layer subsequent tosaid removing.

The method further comprises depositing a first charge carrier transportlayer for transport of charge carriers having the first polarity anddepositing a second charge carrier transport layer for transport ofcharge carriers having said second polarity.

In an embodiment depositing the first charge carrier transport layer issubsequent to depositing the first electrode layer and preceding todepositing the insulating layer and said depositing the second chargecarrier layer is subsequent to depositing the insulating layer andpreceding depositing the resist layer.

In an embodiment, of the method the second charge carrier transportlayer is deposited with an electroplating process and subsequent toremoving the resist layer, and preceding depositing and curing aphoto-electric conversion layer.

In an embodiment the first charge carrier transport layer is depositedwith an electroplating process subsequent to removing the resist layer,and preceding depositing the second charge carrier layer.

The method according to the present invention enables the deposition ofa thicker stack of layers on the first charge carrier transport layerthan would be possible when using the pellet based approach known fromthe prior art. In this way the second charge carrier transport layer canbe provided, therewith significantly improving efficiency of thephoto-voltaic element.

Various methods may be used for depositing and applying layers. Thesemethods may include spin-coating, printing methods, slot-die coating andvapor deposition methods like physical vapor deposition (e.g. E-beamPVD, Sputter PVD), (spatial) Atomic Layer Deposition ((s)ALD), andchemical vapor deposition (e.g. plasma-enhanced chemical vapordeposition (PECVD)).

Etching processes may be applied to remove a material (or a part of thematerial) from a surface either by a chemical reaction generated by theuse of a reactive mix of gases (plasma-etching) or by submerging thesubstrates in a reactive solution where the layer is removed bydissolution or chemical reaction (wet-etching).

A selective etching is made possible by using a mask that locallyprotects the underlying layer(s). A patterning in such a mask may beobtained for example by optical lithography wherein light is used totransfer a geometric pattern from a photo-mask to a light sensitivechemical photoresist on the substrate. Also imprinting can be applied topattern the mask. Alternatively the mask may be directly applied in thedesired pattern, for example by printing.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects are described in more detail with reference tothe drawing. Therein:

FIG. 1A schematically shows a top-view of a semi-finished productobtained during performing a method according to the second aspect,

FIG. 1B shows a cross-section according to IB-IB in FIG. 1A,

FIG. 2A shows a top-view corresponding to the area IIA of asemi-finished product obtained after an additional manufacturing step ofa method according to the second aspect,

FIG. 2B shows a cross-section according to IIB-IIB in FIG. 2A,

FIG. 3A shows a top-view corresponding to the area IIA of asemi-finished product obtained after a further additional manufacturingstep of a method according to the second aspect,

FIG. 3B shows a cross-section according to IIIB-IIIB in FIG. 3A,

FIG. 4A shows a top-view corresponding to the area IIA of asemi-finished product obtained after a still further additionalmanufacturing step of a method according to the second aspect,

FIG. 4B shows a cross-section according to IVB-IVB in FIG. 4A,

FIG. 4C shows in the same cross-section an optional manufacturing stepof a method according to the second aspect,

FIG. 4D shows in the same cross-section an alternative optionalmanufacturing step of a method according to the second aspect,

FIG. 4E shows in the same cross-section a subsequent alternativeoptional manufacturing step of a method according to the second aspect,

FIG. 4F shows in the same cross-section a further subsequent alternativeoptional manufacturing step of a method according to the second aspect,

FIG. 4G shows in the same cross-section an alternative embodimentresulting from a still further subsequent alternative optionalmanufacturing step following the step illustrated in FIG. 4F,

FIG. 5 shows in the same cross-section a first embodiment of aphoto-voltaic element according to the first aspect obtained after afurther manufacturing step of a method according to the second aspect,

FIG. 6 shows in the same cross-section a second embodiment of aphoto-voltaic element according to the first aspect,

FIG. 7 shows in the same cross-section a third embodiment of aphoto-voltaic element according to the first aspect,

FIG. 8A shows a top-view corresponding to the area IIA of a fourthembodiment of a photo-voltaic element according to the first aspect,

FIG. 8B shows a cross-section according to VIIIB-VIIIB in FIG. 8A,

FIG. 9A shows a top-view corresponding to the area IIA of asemi-finished product obtained after an additional manufacturing step ofa method according to the second aspect,

FIG. 9B shows a cross-section according to IXB-IXB in FIG. 9A,

FIG. 10A shows a top-view corresponding to the area IIA of asemi-finished product obtained after an additional manufacturing step ofa method according to the second aspect,

FIG. 10B shows a cross-section according to XB-XB in FIG. 10A,

FIG. 11A shows a top-view corresponding to the area IIA of asemi-finished product obtained after an additional manufacturing step ofa method according to the second aspect,

FIG. 11B shows a cross-section according to XIB-XIB in FIG. 11A,

FIG. 12A shows a top-view corresponding to the area IIA of asemi-finished product obtained after an additional manufacturing step ofa method according to the second aspect,

FIG. 12B shows a cross-section according to XIIB-XIIB in FIG. 12A,

FIG. 12C shows a portion of the surface of the semi-finished product ofFIG. 4B in more detail,

FIG. 12D shows a portion of the surface of the semi-finished product ofFIG. 12B in more detail,

FIG. 13 shows a product obtained after the step of FIG. 12A, 12B,

FIG. 14A shows a top-view corresponding to the area IIA of asemi-finished product obtained after an additional manufacturing step ofa method according to the second aspect,

FIG. 14B shows a cross-section according to XIVB-XIVB in FIG. 14A,

FIG. 15A shows a top-view corresponding to the area IIA of asemi-finished product obtained after an additional manufacturing step ofa method according to the second aspect,

FIG. 15B shows a cross-section according to XVB-XVB in FIG. 15A,

FIG. 16 shows a product obtained after the step of FIG. 15A, 15B,

FIG. 17A shows a top-view corresponding to the area IIA of asemi-finished product obtained after an additional manufacturing step ofa method according to the second aspect,

FIG. 17B shows a cross-section according to XVIIB-XVIIB in FIG. 17A.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 5 schematically shows a photo-voltaic element 1. The photo-voltaicelement 1 comprises a substrate 10 and a stack of layers arrangedthereon. The substrate 10 may be formed of a rigid material such as ametal (e.g. steel, copper or aluminum), silicon or glass or of aflexible material such as a polymer, e.g. a polymer like polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), or polyimide (PI).Also thin metal or glass are suitable substrates. If the substrate isconducting, an isolating layer may be deposited on that substrate toisolate the electrode from the substrate. Dependent on the application athickness of the substrate may be selected in the range of a relativelysmall value e.g. 50 micron and a relatively large value, e.g. a few mmor more. The stack of layers subsequently includes at least a firstelectrode layer 20, a first charge carrier transport layer 30, aninsulating layer 40, a second electrode layer 50, a second chargecarrier transport layer 60, and a photo-electric conversion layer 70.

The first electrode layer 20 is provided for receiving charge carriersof a first polarity. In the embodiment shown the first electrode layer20 is an anode, i.e. arranged for receiving holes as the chargecarriers. Dependent on the lateral size of the photo-voltaic element 1the first electrode layer 20 may for example have a thickness in therange of a few tens to a few hundreds of nanometers or even more. In theembodiment shown the first electrode layer 20 includes an aluminum sublayer having a thickness of 190 nm, which is sandwiched between a pairof nickel layers, each having a thickness of 5 nm. In another examplethe first electrode layer is of molybdenum. In an embodiment where thesubstrate is provided of a metal, it may also serve as a first electrodelayer 20.

In the embodiment shown the first charge carrier transport layer 30 is ahole transport layer, having a thickness in the range of 10 to 200 nm.In the embodiment shown the hole transport layer is formed by anickeloxide layer having a thickness of 50 nm. In another example thehole transport layer is formed by a MoSe layer.

An insulating layer 40 is provided of an organic, e.g. a polymer, orinorganic insulating material, such as a metal oxide. Also a stack ofmaterials can be used. Dependent on the material selected for theinsulating layer, it may have a thickness in the range of 10 to 200 nmfor example, but also a substantially thicker insulating layer may beapplied. In the embodiment shown the insulating layer 40 is provided asa SiO2 layer having a thickness of 100 nm.

A second electrode layer 50 for receiving charge carriers of a secondpolarity opposite to said first polarity is arranged on the insulatinglayer 40. In this case the second electrode layer 50 is a cathode. Anysufficiently conducting material can be used for this purpose at athickness depending on the lateral size of the photo-voltaic element 1.Typically the thickness of the second electrode layer 50 is of the sameorder of magnitude as the thickness of the first electrode layer 20, sothat they have approximately the same conductivity and neither of themforms a bottleneck. In the embodiment shown the second electrode layer50 is an aluminum layer with a thickness of 200 nm. In some embodimentsthe second electrode layer 50 may have a thickness greater than that ofthe first electrode layer 20, e.g. 1.5 times a thickness of the firstelectrode layer 20, to compensate for the presence of the openingsprovided in the second electrode layer 50.

A second charge carrier transport layer 60 for transport of chargecarriers having said the second polarity, opposite to the first polaritylayer is arranged upon the second electrode layer 50. In this case thesecond charge carrier transport layer 60 is an electron transport layer.The second charge carrier transport layer 60, here an electron transportlayer may have a thickness in the range of a few nm, e.g. 5 nm to a fewtens of nm, e.g. 50 nm. In the embodiment shown the second chargecarrier transport layer 60 is a TiO₂ layer having thickness of 15 nm.Other suitable materials for an electron transport layer are for exampleSnO₂, ZrO₂ and ZnO:S.

A photo-electric conversion layer 70 is provided upon the second chargecarrier transport layer 60. The photo-electric conversion layer 70 has aplurality of distributed, typically cylindrical, extensions 72 thatextend through the second charge carrier transport layer 60, the secondelectrode layer 50 and the insulating layer 40 to the first chargecarrier transport layer 30. Therewith the photo-electric conversionlayer 70 is electrically coupled to both the first charge carriertransport layer 30 and the second charge carrier transport layer 60. Inthis arrangement solar radiation R does not need to traverse anelectrode layer or a charge carrier transport layer which contributes toan efficient operation of the photo-voltaic element 1. In the embodimentshown the extensions 72 have an effective cross-section D_(eff) in therange of 0.5 to 10 micron, and have an average pitch in the range of 1.1to 5 times their effective cross-section. The effective cross-section isdefined here as the diameter of a circle having an area corresponding tothe cross-sectional area A_(Ø) of the extensions.

${I.e.\mspace{14mu} D_{eff}} = \sqrt{\frac{4A_{\Phi}}{\pi}}$

The extensions may have any cross-section, such as circular, square ortriangular. Preferably, a circumference O of the extensions is less than10 times the effective diameter D_(eff) and even more preferably lessthan 5 times the effective diameter D_(eff).

In the embodiment the photo-electric conversion layer is provided of aperovskite material, such as methylammonium lead trihalide (CH₃NH₃PbX₃),or Cesium-formamidinum lead trihalide(Cs_(0.05)(H₂NCHNH₂)_(0.95)PbI_(2.85)Br_(0.15)). Alternatively a tinbased perovskite material, such as CH₃NH₃SnI₃ may be used. Also morecomplex perovskite materials may be applied, for example containing acombination of different cations. Also other materials, such as copperindium gallium selenide (CIGS) are suitable.

In the embodiment shown the second electrode layer 50 has anodized edgesurfaces 52 facing the extensions 72 of the photo-electric conversionlayer 70. This avoids direct contact between the second electrode layerand the photo-electric conversion layer.

FIG. 4G illustrates an alternative embodiment wherein such directcontact is avoided. Therein the openings 82 are provided with aninsulating wall 78, e.g. of a ceramic material. The specific steps formanufacturing this embodiment are described in more detail below withreference to FIG. 4D to FIG. 4G.

FIG. 6 shows an embodiment of the photo-voltaic element 1 of theinvention wherein an edge portion 22 of an upper surface of the firstelectrode layer 20 is kept free from material of the first chargecarrier transport layer 30 and is provided with a first electricalcontact 25. Also an edge portion 52 of an upper surface of the secondelectrode layer 50 is kept free from material of the second chargecarrier transport layer 60 and is provided with a second electricalcontact 55. Another possibility is to remove the carrier transport layer30 and isolator 40 with e.g. laser ablation before deposition ofelectrode 50, so a contact can be made from electrode 50 to electrode20. Also before deposition of charge carrier transport layer 30 a laserstep could be used to interrupt the electrode 20.

FIGS. 8A and 8B show a further embodiment of a photo-voltaic elementaccording to the invention. Therein FIG. 8A shows a top-view and FIG. 8Bshows a cross-section of a portion of the device according toVIIIB-VIIIB in FIG. 8A. In this further embodiment the first electrodelayer 20, the first charge carrier transport layer 30, the insulatinglayer 40 and the second electrode layer 50 are provided as a pluralityof layer segments. Therein a plurality of lateral sub-stack segments isformed. By way of example two lateral sub-stack segments A, B are shownin this case. However in practice the photo-voltaic element may have alarger number of lateral sub-stack segments C, D, . . . e.g. 10 or 100or more, depending on a required lateral size of the photo-voltaicelement.

As shown in FIG. 8B each layer segment A,B comprises a first electrodelayer segment 20A, 20B, a first charge carrier transport layer segment30A, 30B, an insulating layer segment 40A, 40B and a second electrodelayer segment 50A, 50B. The second charge carrier transport layer 60 andthe photo-electric conversion layer 70 are formed as continuous layers.A second electrode layer segment 50A of a lateral sub-stack segment Aextends over a first electrode layer segment (20B) in a neighboringsub-stack segment B. Therewith an electrical connection is formedbetween the second electrode layer segment 50A of the lateral sub-stacksegment A and the first electrode layer segment 20B in the neighboringlateral sub-stack segment. In this way the photo-voltaic element isformed as a plurality of serially connected modules, which makes itpossible to reduce resistive losses as compared to a photo-voltaicelement that is not partitioned into serially connected modules. Itcould alternatively be contemplated to serially arrange a plurality ofsmaller photo-voltaic elements. It is however an advantage of theembodiment of FIG. 8A, 8B that external connection elements are avoided.A photo-voltaic element as shown in FIG. 8A, 8B could for example beprovided as a single elongate product applied on a foil, e.g. deliveredin a length of tens to hundreds of meter on a roll.

As shown in FIG. 7 additional layers may be provided. In the embodimentof FIG. 7 for example a barrier 90 is arranged over said photo-electricconversion layer 70. Suitable materials for the barrier are metaloxides, such as SiOx and SiNx. In practice the barrier 90 may comprise aplurality of layers, such as a stack of inorganic layers having amutually different composition. Also a combination of inorganic layersand organic layers may be used. For example a barrier 90 may be formedby a first and a second inorganic layer that sandwich an organic layer.For a good light in coupling it is preferred that the materials used forthe barrier 90 have a refractive index lower than that of thephoto-electric conversion layer 70.

In the embodiment shown light in coupling is further improved by a lightin coupling structure 100 arranged over the barrier 90. In theembodiment shown the light in coupling structure comprises a pluralityof light in coupling elements 102A, 102B. For example semi-spherical orpyramidal shaped light in coupling elements may be used.

A method of manufacturing a photo-voltaic element is now disclosed withreference to FIGS. 1 to 5.

FIG. 1A, 1B show the intermediate product obtained after a first threesteps. Therein FIG. 1A shows a top-view and FIG. 1B shows across-section according to IB-IB in FIG. 1A.

Therein a substrate is 10 is provided in a first step S1. Then in asecond step S2 a stack of layers is deposited thereon that comprise atleast in the order named a first electrode layer 20, a first chargecarrier transport layer 30, an insulating layer 40, a second electrodelayer 50 and a second charge carrier transport layer.

The first electrode layer 20 is provided for receiving charge carriersof a first polarity. The first electrode layer 20 may for example be ananode, i.e. arranged for receiving holes as the charge carriers.Alternatively the first electrode layer 20 may be a cathode, i.e.arranged for receiving electrons as the charge carriers. In anembodiment the first electrode layer 20 is deposited with a PVD(physical vapor deposition) method, for example using E-beam PVD. Inthis example the first electrode layer 20 was provided as a stack ofsub-layers obtained by subsequently depositing a first sub-layer ofnickel having a thickness of 5 nm, an aluminum layer having a thicknessof 190 nm and a second sub-layer of nickel also having a thickness of 5nm. Then spin-coating (1000 rpm) was used to deposit a NiO layer as thefirst charge carrier transport layer 30, here a hole transport layer.

An insulating layer 40 was then deposited in a first and a second stage.In the first of these stages a first, 100 nm thick, sublayer of SiOx wasdeposited by electron-beam deposition and in the second stage a secondsublayer of SiOx, also having a thickness of 100 nm was deposited byPECVD. Then a second electrode layer 50, here a cathode layer ofaluminum at a thickness of 200 nm was formed using the same method andconditions as those applied for the deposition of the aluminum sub-layerof the first electrode layer 20.

A second charge carrier transport layer 60, here an electron transportlayer was then deposited. In this case electron-beam vapor depositionwas used to deposit a TiOx layer with a thickness of 15 nm of lineartitanium dioxide (TiOx).

The insulating layer 40 and the layers 50, 60 form a sub-stack having anupper surface 64. In a third step S3, here using spin coating a resistlayer 80, here a photo-resist layer having a thickness of 1.6 micron wasdeposited on this upper surface 64. In other implementations the resistlayer may be an imprint-resist layer.

FIG. 2A, 2B show a subsequent step S4. Therein FIG. 2A shows a top-viewof an intermediate product resulting from this step S4 and FIG. 2B showsa cross-section according to IIB-IIB in FIG. 2A. In this subsequent stepregularly distributed openings 82 giving access to the upper surface 64are formed in the resist layer 80. In this embodiment contactlithography was used for this purpose. Using the method describedherewith samples were prepared having openings with diameter in therange of 0.5-5 μm and a distance between neighboring openings in therange of 1-5 μm. Therewith a pitch between 1 and 10 gm is obtained. Theopenings having an effective cross-section D in the range of 0.5 to 10micron, and have an average pitch in the range of 1.1 to 5 times theeffective cross-section.

Instead of patterning an originally homogeneous resist layer, it isalternatively possible to directly depositing the resist layer in thedesired pattern, for example using a printing technique.

FIGS. 3A and 3B show a subsequent step S5, wherein material of thesub-stack 40, 50, 60 facing the openings 82 is selectively removed.Therein FIG. 3A shows a top-view of the semi-finished product obtainedafter this step S5 and FIG. 3B shows a cross-section according toIIIB-IIIB in FIG. 3A. Step S5 involves etching the upper layers 50, 60by plasma etching. Then the insulating SiOx layer is etched with afurther plasma etching process. The photo-resist layer 80 is then fullyremoved (Step S6), for example by oxygen plasma-etching as illustratedin FIGS. 4A and 4B. Therein FIG. 4A is a top-view and FIG. 4B shows across-section according to IVB-IVB in FIG. 4A.

As shown in FIG. 5, in a step S7, subsequent to this step S6, aphoto-electric conversion layer 70 is deposited (for example byspin-coating) and cured.

Optional pre-processing steps, S6A and S6B may be performed afterremoval of the resist layer 80 and before deposition of thephoto-electric conversion layer 70.

A first optional pre-processing step S6A is illustrated in FIG. 4B.Therein an edge surface 52 of the second electrode layer 50 is anodized.This edge surface 52 was formed by the step of etching S5. Thisanodization process an insulating layer is formed on the edge surface 52therewith avoiding a direct contact between the second electrode layer50 and the photo-electric conversion layer 70.

FIG. 4C illustrates a second optional pre-processing step S6B. Thereinto facilitate the deposition in step S7, an atomic layer depositionprocess (ALD) may be used to deposit a thin growth layer 74, e.g.applying a TiO₂ layer with a few sALD cycles.

FIG. 4D-4G shows an alternative approach for preventing a directelectrical contact between the second electrode layer 50 and thephoto-electric conversion layer 70. After removal (S6) of the patternedresist layer 80 as shown in FIG. 4D, a layer 76 of an insulatingmaterial is conformally deposited (Step S6C) on the semi-finishedproduct of FIG. 4D, therewith obtaining the semifinished product of FIG.4E. Then an anisotropic etch step S6D, e.g. a plasma etch step isapplied. The anisotropic etch step 56D removes the insulating materialfrom the surface of the second charge carrier transport layer 60 andfrom the surface portions of the first charge carrier transport layer 30within the openings 82 but keeps a layer of the insulating material onthe walls of the openings 82 intact. Subsequent to this step S6D thephoto-electric conversion layer can be deposited (S6E) as shown in FIG.4G.

Upon completion the substrate 10 may be removed. For example this may bethe case if an electrode layer, e.g. the first electrode layer 20provides sufficient structural integrity. Alternatively, or in additionmechanical support may be provided by further layers applied on thephoto-electric conversion layer 70.

FIGS. 9A, 9B, 10A, 10B, 11A, 11B, 12A, 12B and 13 show a furtheralternative embodiment of a method of manufacturing. Therein FIG. 9A, 9Bshow a semi-finished product that is obtained after step S15 of thisembodiment. The steps of this embodiment up to and including S15 of thisembodiment correspond to those disclosed herein for steps S1-S5 of theembodiment of FIGS. 1A, 1B, 2A, 2B and 3A, 3B, except for the fact thatthe step corresponding to step S2, does not include deposition of acharge carrier transport layer 60. Instead the charge carrier transportlayer 60 is deposited in another stage of the process as is discussedwith reference to FIG. 12A, 12B. Following step S15, in step S16 shownin FIG. 10A, 10B, an opening 54 is formed in the second electrode layer50. This can be achieved by a wet etching step selected for the secondelectrode layer 50. For example using a PES (Phosphoric Acid, AceticAcid, Sulphoric acid The last is now often replaced with Nitric acid)solution in case of a second electrode 50 formed by an aluminum layer orhaving an aluminum layer as a main layer which is sandwiched betweenauxiliary layers, e.g. formed by molybdenum. Alternatively, if thesecond electrode 50 is formed by conductive oxide layer, such as ITO, aHCL-FeCl solution may be used as the etching agent. Still alternativelyan isotropic or anisotropic plasma etching step may be used in stepS16A.

In a next step S16B, as shown in FIG. 11A, 11B, an opening 44 is formedin the insulating layer 40, to expose the surface of the charge carriertransport layer 30. An isotropic plasma etching step, for example usingCF₄/O₂ may be applied. Also wet etching can be used. E.G. NH₄F if asiliconoxide isolator is used.

In a further step S16C, a second charge carrier transport layer 60, isdeposited in an electroplating process, therewith using the layer 50 asthe electrode. Due to the curved edge 55 of the opening formed in theelectrode 50, an increased electric field is obtained that enhances thedeposition speed near the opening. By way of example, a hole transportlayer may be deposited as the charge carrier transport layer 60, e.g.CuSCN using a solution of CuSO4/Nitrilotriacetic acid/KSCN.Alternatively, the charge carrier transport layer 60 may be depositedfrom an ionic liquid.

Then in step S17, which is comparable to step S7 as disclosed withreference to FIG. 5, a photo-electric conversion layer 70 is deposited.

In the photo-voltaic element so obtained, the extensions 72 taperoutward in a direction from the first charge carrier transport layer 30towards the second charge carrier layer 60. As a result of theelectroplating process used for the second charge carrier transportlayer 60, the material thereof covers a surface of the second electrode50 surrounding the extensions 72. Using an isotropic etching process,the openings formed will taper outward towards the second charge carrierlayer 60 with an angle of approximately 45 degrees, so that theperimeter of the opening at the contact-surface of the first chargecarrier transport layer is displaced with respect to the perimeter atthe level of the surface of the second charge carrier transport layer isof the order of magnitude of the total thickness of the layers in whichthe opening is formed. For example, if the effective cross-sectionD_(eff) of the opening with which the first charge carrier layer 30 isto be exposed, as defined by the mask used for etching is 1 micron, andthe thicknesses of the second electrode layer 50 and the insulatinglayer 40 are 100 nm and 300 nm respectively, then at the plane surfaceof the second charge carrier transport layer 60, the cross-section Doutmay be about 1.8 micron. As the electroplated second charge carrierlayer 60 also has a portion 65 that extends over the tapering wall ofthe opening the contact surface of the second charge carrier layer 60available for the photovoltaic layer 70 to be deposited in the next stepis increased as compared to the situation in FIG. 4B for example. In theembodiment of FIG. 12B, the available contact surface At formed by thetapering hole in the second charge carrier transport layer is

At=πH(Deff+αH), wherein H is the height of the electrode layer 50 and αis the inclination factor with which the diameter widens towards thesurface 67 of the second charge carrier transport layer 60. I.e. theinclination factor α is defined by

α=(Dout−Deff)/2H.

This additional surface At is illustrated as the hatched are At in FIG.12D This is compared with the situation in FIG. 4B. In that case, anannulus having an inner diameter Deff and an outer diameter Dout wouldbe additionally available at the surface 67 of the second charge carriertransport layer. The surface Ac of this area between the dashed circlein FIG. 12C and area removed by the opening to give access to the firstcharge carrier transport layer 30 is equal to

Ac=1/2 παDH+πα ² H ²

Hence the difference in the surface At and the surface Ac is equal to

ΔA=At−Ac=π(1−α/2)DH+πα(1−α)H ²

Accordingly, if a is in a range between 0 and 1, the contact surfacearea of the second charge carrier layer 60 is always improved.Furthermore an improvement may be obtained in the range 1<α<2, providedthat: π(1−α/2)D>πα(1−α)H. It is noted that the height of the secondcharge carrier transport layer 60 typically is substantially smallerthan the height of the second electrode layer. However, for visibilitythe height of this layer 60 is exaggerated.

An alternative embodiment of the method is illustrated in FIG. 14A, 14B,15A, 16B.

The preparatory steps with which the semi-finished product as shown inFIG. 14A, 14B is obtained after step S26, differ from those used for thesemi-finished product of FIG. 11A, 11B, in that no first charge-carriertransport layer 30 is deposited. Instead, in the subsequent step S27 asshown in FIG. 15A, 15B, the first charge-carrier transport layer 30 isdeposited locally on the exposed portions of the surface of the firstelectrode layer 20, using an electroplating process. E.g. electroplatingof an ETL like SnO₂ from a solution of 20 mM tin chloride (SnCl₂) and 75mM nitric acid Starting from here, also the second charge-carriertransport layer 60 can be deposited, as shown in FIG. 12A, 12B and aphoto-electric conversion layer 70 can be deposited as shown in FIG. 13.The second charge carrier transport layer, in this case a HTL, may bedeposited for example from CuSCN using a solution ofCuSO4/Nitrilotriacetic acid/KSCN. The product so obtained, as shown inFIG. 16, is characterized in that the first charge carrier layer 30 isabsent in areas of the first electrode layer 20 covered by theinsulating layer 40. In an alternative embodiment, electrodeposition maybe used to deposit a hole transport layer as the first charge carriertransport layer 30 and to deposit an electron transport layer as thesecond charge carrier transport layer 60.

It is still further possible that only the first charge-carrier layer 30is deposited by electro-plating. For example, starting from asemi-finished product, differing from the semi-finished product of FIG.2A, 2B, in that a first charge carrier transport layer 30 is absent, anopening may be formed in the layers 40, 50 and 60 in steps as describedwith reference to FIG. 3A, 3B, or as described with reference to FIG.10A, 10B, 11A, 11B, and subsequently an electro-plating step S37 can beused to deposit a first charge carrier layer 30 on the exposed portionsof the surface of the first electrode 20, as shown in FIG. 17A, 17B.Also in this case, the product which is obtained is characterized inthat the first charge carrier layer 30 is absent in areas of the firstelectrode layer 20 covered by the insulating layer 40.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative and exemplary and not restrictive; theinvention is not limited to the disclosed embodiments. Other variationsto the disclosed embodiments can be understood and effected by thoseskilled in the art in practicing the claimed invention, from a study ofthe drawings, the disclosure and the appended claims.

In the claims the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. A single processor or other unit may fulfill the functions ofseveral items recited in the claims. The mere fact that certain measuresare recited in mutually different claims does not indicate that acombination of these measures cannot be used to advantage. Any referencesigns in the claims should not be construed as limiting the scope.

1. A photo-voltaic element comprising a stack of layers, the stack oflayers at least including the following layers arranged in the ordernamed: a first electrode layer for receiving charge carriers of a firstpolarity, a first charge carrier transport layer, for transport ofcharge carriers having said first polarity, an insulating layer, asecond electrode layer for receiving charge carriers of a secondpolarity opposite to said first polarity, a second charge carriertransport layer, for transport of charge carriers having said secondpolarity, a photo-electric conversion layer, wherein charge carriers ofthe first polarity have a first mobility and wherein charge carriers ofthe second polarity have a second mobility, the photo-electricconversion layer comprising a plurality of distributed extensionsextending through said second charge carrier transport layer, saidsecond electrode layer and said insulating layer to the first chargecarrier transport layer, the extensions having an effectivecross-section D_(eff) in the range of 0.5 to 10 micron, and having anaverage pitch in the range of 1.1 to 5 times said effectivecross-section, the effective cross-section being a diameter of a circlehaving an area corresponding to the cross-sectional area A_(Ø) of theextensions, and the extensions having a circumference O that is lessthan 10 times the effective diameter D_(eff), a contact-surface of thephoto-electric conversion layer with the first charge carrier transportlayer having a first surface area, and a contact-surface of thephoto-electric conversion layer with the second charge carrier transportlayer having a second surface area, a ratio between the second surfacearea and the first surface area being approximately equal to a ratiobetween the first mobility and the second mobility.
 2. The photo-voltaicelement according to claim 1, wherein said second electrode layer hasanodized edge surfaces facing the extensions of the photo-electricconversion layer.
 3. The photo-voltaic element according to claim 1,wherein an insulating material is provided around said extensions,forming an insulating wall between said second electrode layer and saidphoto-electric conversion layer.
 4. The photo-voltaic element accordingto claim 1, further comprising a growth layer at an interface betweensaid photo-electric conversion layer and said second charge carriertransport layer as well as at an interface between said extensions ofthe photo-electric conversion layer and each of edge surfaces of saidsecond charge carrier transport layer, said second electrode layer andsaid insulating layer and at an interface between said extensions of thephoto-electric conversion layer and the first charge carrier transportlayer.
 5. The photo-voltaic element according to claim 1, wherein thephoto-electric conversion layer is provided of a perovskite material. 6.The photo-voltaic element according to claim 1, wherein thephoto-electric conversion layer is made of copper indium galliumselenide (CIGS).
 7. The photo-voltaic element according to claim 1,wherein an edge portion of an upper surface of the first electrode layeris kept free from material of the first charge carrier transport layerand is provided with a first electrical contact and or an edge portionof an upper surface of the second electrode layer is kept free frommaterial of the second charge carrier transport layer and is providedwith a second electrical contact.
 8. The photo-voltaic element accordingto claim 1, wherein said first electrode layer, said first chargecarrier transport layer, said insulating layer and said second electrodelayer are provided as a plurality of layer segments, wherein a pluralityof lateral sub-stack segments each comprise a respective first electrodelayer segment, a first charge carrier transport layer segment, aninsulating layer segment and a second electrode layer segment, wherein asecond electrode layer segment of a lateral sub-stack segment extendsover a first electrode layer segment n a neighboring sub-stack segment,therewith forming an electrical connection between said second electrodelayer segment of said lateral sub-stack segment and said first electrodelayer segment in said neighboring lateral sub-stack segment.
 9. Thephoto-voltaic element according to claim 1, wherein the extensions taperoutward in a direction from the first charge carrier transport layertowards the second charge carrier layer.
 10. The photo-voltaic elementaccording to claim 9, wherein a material of the second charge carriertransport layer covers a surface of the second electrode surrounding theextensions.
 11. The photo-electric element according to claim 1, whereinthe first charge carrier layer is absent in areas of the first electrodelayer covered by the insulating layer.
 12. Method of manufacturing aphoto-voltaic element comprising the steps of: providing a substrate;depositing thereon a stack of layers comprising at least in the ordernamed: a first electrode layer for receiving charge carriers of a firstpolarity; a first charge carrier transport layer, for transport ofcharge carriers having said first polarity; an insulating layer; asecond charge carrier transport layer, for transport of charge carriershaving a second polarity opposite to said first polarity; a secondelectrode layer for receiving charge carriers of the second polarity;wherein the insulating layer and layers subsequently deposited in thisstep form a substack having an upper surface, applying a resist layer onsaid upper surface, wherein said resist layer is provided with aplurality of distributed openings towards said upper surface, theopenings having an effective cross-section D in the range of 0.5 to 10micron, and having an average pitch in the range of 1.1 to 5 times saideffective cross-section, the effective cross-section being a diameter ofa circle having an area corresponding to the cross-sectional area A_(Ø)of the extensions, and the extensions having a circumference O that isless than 10 times the effective diameter D_(eff), etching toselectively remove material of the sub-stack facing the openings,removing the resist layer subsequent to said etching, depositing andcuring a photo-electric conversion layer subsequent to said removingwherein a contact-surface of the photo-electric conversion layer withthe first charge carrier transport layer has a first surface area, and acontact-surface of the photo-electric conversion layer with the secondcharge carrier transport layer has a second surface area, and a ratiobetween the second surface area and the first surface area isapproximately equal to a ratio between a first mobility of the chargecarriers having said first polarity and a second mobility of the chargecarriers having said second polarity. 13-14. (canceled)
 15. The methodaccording to claim 12, wherein the second charge carrier transport layeris deposited with an electroplating process and subsequent to removingthe resist layer, and preceding depositing and curing a photo-electricconversion layer.
 16. The method according to claim 12, wherein thefirst charge carrier transport layer is deposited with an electroplatingprocess.
 17. The method according to claim 12, further comprisinganodizing an edge surface of the second electrode layer resulting fromsaid etching, said anodizing being performed prior to the step ofdepositing the photo-electric conversion layer.
 18. The method accordingto claim 12, further comprising conformally depositing a layer of aninsulating material subsequent to said step of etching andanisotropically etching said layer to removes the insulating materialfrom the surface of the second charge carrier transport layer and fromthe surface portions of the first charge carrier transport layer withinthe openings while keeping a layer of the insulating material on thewalls of the openings intact.
 19. The method according to claim 12,further comprising depositing a growth layer subsequent to said step ofetching and prior to the step of depositing the photo-electricconversion layer.
 20. The method according to claim 12, furthercomprising depositing a barrier over said photo-electric conversionlayer.
 21. (canceled)
 22. The method according to claim 20, comprisingapplying a light in coupling structure over said barrier.
 23. (canceled)24. The method according to claim 12, wherein the photo-electricconversion layer is provided of a perovskite material or of copperindium gallium selenide (CIGS).